draft-ietf-ippm-connectivity-01.txt   draft-ietf-ippm-connectivity-02.txt 
Network Working Group J. Mahdavi, Pittsburgh Supercomputer Center Network Working Group J. Mahdavi, Pittsburgh Supercomputer Center
Internet Draft V. Paxson, Lawrence Berkeley National Laboratory Internet Draft V. Paxson, Lawrence Berkeley National Laboratory
Expiration Date: May 1998 November 1997 Expiration Date: February 1999 August 1998
Connectivity IPPM Metrics for Measuring Connectivity
<draft-ietf-ippm-connectivity-01.txt> <draft-ietf-ippm-connectivity-02.txt>
1. Status of this Memo 1. Status of this Memo
This document is an Internet Draft. Internet Drafts are working This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet Drafts. working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six Internet Drafts are draft documents valid for a maximum of six
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To learn the current status of any Internet Draft, please check the To view the entire list of current Internet-Drafts, please check the
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munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific
ftp.isi.edu (US West Coast). Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).
This memo provides information for the Internet community. This memo This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of does not specify an Internet standard of any kind. Distribution of
this memo is unlimited. this memo is unlimited.
2. Introduction 2. Introduction
Connectivity is the basic stuff from which the Internet is made. Connectivity is the basic stuff from which the Internet is made.
Therefore, metrics determining whether pairs of hosts (IP addresses) Therefore, metrics determining whether pairs of hosts (IP addresses)
can reach each other must form the base of a measurement suite. We can reach each other must form the base of a measurement suite. We
define several such metrics, some of which serve mainly as building define several such metrics, some of which serve mainly as building
blocks for the others. blocks for the others.
This memo defines a series of metrics for connectivity between a pair This memo defines a series of metrics for connectivity between a pair
of Internet hosts. It builds on notions introduced and discussed in of Internet hosts. It builds on notions introduced and discussed in
the revised IPPM Framework document (currently <draft-ietf-ippm- RFC 2330, the IPPM framework document. The reader is assumed to be
framework-01.txt>); the reader is assumed to be familiar with that familiar with that document.
document.
The structure of the memo is as follows: The structure of the memo is as follows:
ID Connectivity November 1997 ID IPPM Metrics for Measuring Connectivity August 1998
+ An analytic metric, called Type-P-Instantaneous-Unidirectional- + An analytic metric, called Type-P-Instantaneous-Unidirectional-
Connectivity, will be introduced to define one-way connectivity at Connectivity, will be introduced to define one-way connectivity at
one moment in time. one moment in time.
+ Using this metric, another analytic metric, called Type-P- + Using this metric, another analytic metric, called Type-P-
Instantaneous-Bidirectional-Connectivity, will be introduced to Instantaneous-Bidirectional-Connectivity, will be introduced to
define two-way connectivity at one moment in time. define two-way connectivity at one moment in time.
+ Using these metrics, corresponding one- and two-way analytic + Using these metrics, corresponding one- and two-way analytic
metrics are defined for connectivity over an interval of time. metrics are defined for connectivity over an interval of time.
+ Using these metrics, an analytic metric, called Type-P1-P2- + Using these metrics, an analytic metric, called Type-P1-P2-
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3.3. Metric Units: 3.3. Metric Units:
Boolean. Boolean.
3.4. Definition: 3.4. Definition:
Src has *Type-P-Instantaneous-Unidirectional-Connectivity* to Dst at Src has *Type-P-Instantaneous-Unidirectional-Connectivity* to Dst at
time T if a type-P packet transmitted from Src to Dst at time T will time T if a type-P packet transmitted from Src to Dst at time T will
arrive at Dst. arrive at Dst.
ID Connectivity November 1997 ID IPPM Metrics for Measuring Connectivity August 1998
3.5. Discussion: 3.5. Discussion:
This metric is probably not directly useful, because it is For most applications (e.g., any TCP connection) bidirectional
instantaneous and unidirectional. For most applications, connectivity is considerably more germane than unidirectional
bidirectional connectivity is considerably more germane (e.g., any connectivity, although unidirectional connectivity can be of interest
TCP connection). Most applications also require connectivity over an for some security applications (e.g., testing whether a firewall
interval. Finally, one might not have instantaneous connectivity due correctly filters out a "ping of death"). Most applications also
to a transient event such as a full queue at a router, even if at require connectivity over an interval, while this metric is
nearby instants in time one does have connectivity. These points are instantaneous, though, again, for some security applications
addressed below, with this metric serving as a building block. instantaneous connectivity remains of interest. Finally, one might
not have instantaneous connectivity due to a transient event such as
a full queue at a router, even if at nearby instants in time one does
have connectivity. These points are addressed below, with this
metric serving as a building block.
Note also that we have not explicitly defined *when* the packet Note also that we have not explicitly defined *when* the packet
arrives at Dst. The TTL field in IP packets is meant to limit IP arrives at Dst. The TTL field in IP packets is meant to limit IP
packet lifetimes to 255 seconds (RFC 791). In practice the TTL field packet lifetimes to 255 seconds (RFC 791). In practice the TTL field
can be strictly a hop count (RFC 1812), with most Internet hops being can be strictly a hop count (RFC 1812), with most Internet hops being
much shorter than one second. This means that most packets will have much shorter than one second. This means that most packets will have
nowhere near the 255 second lifetime. In principle, however, it is nowhere near the 255 second lifetime. In principle, however, it is
also possible that packets might survive longer than 255 seconds. also possible that packets might survive longer than 255 seconds.
Consideration of packet lifetimes must be taken into account in Consideration of packet lifetimes must be taken into account in
attempts to measure the value of this metric. attempts to measure the value of this metric.
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have connectivity to Src. Such a methodology could reliably measure have connectivity to Src. Such a methodology could reliably measure
the unidirectional connectivity defined in this metric. the unidirectional connectivity defined in this metric.
4. Instantaneous Two-way Connectivity 4. Instantaneous Two-way Connectivity
4.1. Metric Name: 4.1. Metric Name:
Type-P-Instantaneous-Bidirectional-Connectivity Type-P-Instantaneous-Bidirectional-Connectivity
4.2. Metric Parameters: 4.2. Metric Parameters:
ID IPPM Metrics for Measuring Connectivity August 1998
+ A1, the IP address of a host + A1, the IP address of a host
+ A2, the IP address of a host + A2, the IP address of a host
+ T, a time + T, a time
ID Connectivity November 1997
4.3. Metric Units: 4.3. Metric Units:
Boolean. Boolean.
4.4. Definition: 4.4. Definition:
Addresses A1 and A2 have *Type-P-Instantaneous-Bidirectional- Addresses A1 and A2 have *Type-P-Instantaneous-Bidirectional-
Connectivity* at time T if address A1 has Type-P-Instantaneous- Connectivity* at time T if address A1 has Type-P-Instantaneous-
Unidirectional-Connectivity to address A2 and address A2 has Type-P- Unidirectional-Connectivity to address A2 and address A2 has Type-P-
Instantaneous-Unidirectional-Connectivity to address A1. Instantaneous-Unidirectional-Connectivity to address A1.
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development of interval-connectivity metrics below. development of interval-connectivity metrics below.
5. One-way Connectivity 5. One-way Connectivity
5.1. Metric Name: 5.1. Metric Name:
Type-P-Interval-Unidirectional-Connectivity Type-P-Interval-Unidirectional-Connectivity
5.2. Metric Parameters: 5.2. Metric Parameters:
+ Src, the IP address of a host + Src, the IP address of a host
ID IPPM Metrics for Measuring Connectivity August 1998
+ Dst, the IP address of a host + Dst, the IP address of a host
+ T, a time + T, a time
+ dT, a duration + dT, a duration
{Comment: Thus, the closed interval [T, T+dT] denotes a time {Comment: Thus, the closed interval [T, T+dT] denotes a time
interval.} interval.}
ID Connectivity November 1997
5.3. Metric Units: 5.3. Metric Units:
Boolean. Boolean.
5.4. Definition: 5.4. Definition:
Address Src has *Type-P-Interval-Unidirectional-Connectivity* to Address Src has *Type-P-Interval-Unidirectional-Connectivity* to
address Dst during the interval [T, T+dT] if for some T' within [T, address Dst during the interval [T, T+dT] if for some T' within [T,
T+dT] it has Type-P-instantaneous-connectivity to Dst. T+dT] it has Type-P-instantaneous-connectivity to Dst.
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Boolean. Boolean.
6.4. Definition: 6.4. Definition:
Addresses A1 and A2 have *Type-P-Interval-Bidirectional-Connectivity* Addresses A1 and A2 have *Type-P-Interval-Bidirectional-Connectivity*
between them during the interval [T, T+dT] if address A1 has Type-P- between them during the interval [T, T+dT] if address A1 has Type-P-
Interval-Unidirectional-Connectivity to address A2 during the Interval-Unidirectional-Connectivity to address A2 during the
interval and address A2 has Type-P-Interval-Unidirectional- interval and address A2 has Type-P-Interval-Unidirectional-
Connectivity to address A1 during the interval. Connectivity to address A1 during the interval.
ID Connectivity November 1997 ID IPPM Metrics for Measuring Connectivity August 1998
6.5. Discussion: 6.5. Discussion:
This metric is not quite what's needed for defining "useful" This metric is not quite what's needed for defining "generally
connectivity - that requires the notion that a packet sent from A1 to useful" connectivity - that requires the notion that a packet sent
A2 can elicit a response from A2 that will reach A1. With this from A1 to A2 can elicit a response from A2 that will reach A1. With
definition, it could be that A1 and A2 have full-connectivity but this definition, it could be that A1 and A2 have full-connectivity
only, for example, at at time T1 early enough in the interval [T, but only, for example, at at time T1 early enough in the interval [T,
T+dT] that A1 and A2 cannot reply to packets sent by the other. This T+dT] that A1 and A2 cannot reply to packets sent by the other. This
deficiency motivates the next metric. deficiency motivates the next metric.
7. Two-way Temporal Connectivity 7. Two-way Temporal Connectivity
7.1. Metric Name: 7.1. Metric Name:
Type-P1-P2-Interval-Temporal-Connectivity Type-P1-P2-Interval-Temporal-Connectivity
7.2. Metric Parameters: 7.2. Metric Parameters:
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Address Src has *Type-P1-P2-Interval-Temporal-Connectivity* to Address Src has *Type-P1-P2-Interval-Temporal-Connectivity* to
address Dst during the interval [T, T+dT] if there exist times T1 and address Dst during the interval [T, T+dT] if there exist times T1 and
T2, and time intervals dT1 and dT2, such that: T2, and time intervals dT1 and dT2, such that:
+ T1, T1+dT1, T2, T2+dT2 are all in [T, T+dT]. + T1, T1+dT1, T2, T2+dT2 are all in [T, T+dT].
+ T1+dT1 <= T2. + T1+dT1 <= T2.
+ At time T1, Src has Type-P1 instantanous connectivity to Dst. + At time T1, Src has Type-P1 instantanous connectivity to Dst.
+ At time T2, Dst has Type-P2 instantanous connectivity to Src. + At time T2, Dst has Type-P2 instantanous connectivity to Src.
+ dT1 is the time taken for a Type-P1 packet sent by Src at time T1 + dT1 is the time taken for a Type-P1 packet sent by Src at time T1
to arrive at Dst. to arrive at Dst.
ID Connectivity November 1997 ID IPPM Metrics for Measuring Connectivity August 1998
+ dT2 is the time taken for a Type-P2 packet sent by Dst at time T2 + dT2 is the time taken for a Type-P2 packet sent by Dst at time T2
to arrive at Src. to arrive at Src.
7.5. Discussion: 7.5. Discussion:
This metric defines "useful" connectivity -- Src can send a packet to This metric defines "generally useful" connectivity -- Src can send a
Dst that elicits a response. Because many applications utilize packet to Dst that elicits a response. Because many applications
different types of packets for forward and reverse traffic, it is utilize different types of packets for forward and reverse traffic,
possible (and likely) that the desired responses to a Type-P1 packet it is possible (and likely) that the desired responses to a Type-P1
will be of a different type Type-P2. Therefore, in this metric we packet will be of a different type Type-P2. Therefore, in this
allow for different types of packets in the forward and reverse metric we allow for different types of packets in the forward and
directions. reverse directions.
7.6. Methodologies: 7.6. Methodologies:
Here we sketch a class of methodologies for estimating Type-P1-P2- Here we sketch a class of methodologies for estimating Type-P1-P2-
Interval-Temporal-Connectivity. It is a class rather than a single Interval-Temporal-Connectivity. It is a class rather than a single
methodology because the particulars will depend on the types P1 and methodology because the particulars will depend on the types P1 and
P2. P2.
7.6.1. Inputs: 7.6.1. Inputs:
+ Types P1 and P2, addresses A1 and A2, interval [T, T+dT]. + Types P1 and P2, addresses A1 and A2, interval [T, T+dT].
skipping to change at page 8, line 5 skipping to change at page 8, line 5
dT = 60 seconds. dT = 60 seconds.
W = 10 seconds. W = 10 seconds.
N = 20 packets. N = 20 packets.
7.6.3. Algorithm: 7.6.3. Algorithm:
+ Compute N *sending-times* that are randomly, uniformly distributed + Compute N *sending-times* that are randomly, uniformly distributed
over [T, T+dT-W]. over [T, T+dT-W].
ID Connectivity November 1997 ID IPPM Metrics for Measuring Connectivity August 1998
+ At each sending time, transmit from A1 a well-formed packet of + At each sending time, transmit from A1 a well-formed packet of
type P1 to A2. type P1 to A2.
+ Inspect incoming network traffic to A1 to determine if a + Inspect incoming network traffic to A1 to determine if a
successful reply is received. The particulars of doing so are successful reply is received. The particulars of doing so are
dependent on types P1 & P2, discussed below. If a successful dependent on types P1 & P2, discussed below. If a successful
reply is received, the value of the measurement is "true". reply is received, the value of the measurement is "true".
+ If no successful replies are received by time T+dT, the value of + If no successful replies are received by time T+dT, the value of
the measurement is "false". the measurement is "false".
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probably should be addressed with another metric). probably should be addressed with another metric).
+ An ICMP port-unreachable from A2 to A1 indicates temporal + An ICMP port-unreachable from A2 to A1 indicates temporal
connectivity between the addresses (and again a *lack* of service connectivity between the addresses (and again a *lack* of service
connectivity for TCP-port-N1-port-N2). {Comment: TCP connectivity for TCP-port-N1-port-N2). {Comment: TCP
implementations generally do not need to send ICMP port- implementations generally do not need to send ICMP port-
unreachable messages because a separate mechanism is available unreachable messages because a separate mechanism is available
(sending a RST). However, RFC 1122 states that a TCP receiving an (sending a RST). However, RFC 1122 states that a TCP receiving an
ICMP port-unreachable MUST treat it the same as the equivalent ICMP port-unreachable MUST treat it the same as the equivalent
transport-level mechanism (for TCP, a RST).} transport-level mechanism (for TCP, a RST).}
ID Connectivity November 1997 ID IPPM Metrics for Measuring Connectivity August 1998
+ An ICMP host-unreachable or network-unreachable to A1 (not + An ICMP host-unreachable or network-unreachable to A1 (not
necessarily from A2) with an enclosed IP header matching that sent necessarily from A2) with an enclosed IP header matching that sent
from A1 to A2 *suggests* a lack of temporal connectivity. If by from A1 to A2 *suggests* a lack of temporal connectivity. If by
time T+dT no evidence of temporal connectivity has been gathered, time T+dT no evidence of temporal connectivity has been gathered,
then the receipt of the ICMP can be used as additional information then the receipt of the ICMP can be used as additional information
to the measurement value of "false". to the measurement value of "false".
{Comment: Similar methodologies are needed for ICMP Echo, UDP, etc.} {Comment: Similar methodologies are needed for ICMP Echo, UDP, etc.}
8. Security Considerations 8. Security Considerations
This memo raises no security issues. As noted in RFC 2330, active measurement techniques, such as those
defined in this document, can be abused for denial-of-service attacks
disguised as legitimate measurement activity. Furthermore, testing
for connectivity can be used to probe firewalls and other security
mechnisms for weak spots.
9. References 9. References
F. Baker, "Requirements for IP Version 4 Routers", RFC 1812, June F. Baker, "Requirements for IP Version 4 Routers", RFC 1812, June
1995. 1995.
R. Braden, "Requirements for Internet hosts - communication layers", R. Braden, "Requirements for Internet hosts - communication layers",
RFC 1122, October 1989. RFC 1122, October 1989.
V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, Paxson, "Framework V. Paxson, G. Almes, J. Mahdavi, and M. Mathis, Paxson, "Framework
for IP Performance Metrics", Internet Draft <draft-ietf-ippm- for IP Performance Metrics", RFC 2330, May 1998.
framework-01.txt>, November 1996.
J. Postel, "Internet Protocol", RFC 791, September 1981. J. Postel, "Internet Protocol", RFC 791, September 1981.
10. Authors' Addresses 10. Authors' Addresses
Jamshid Mahdavi <mahdavi@psc.edu> Jamshid Mahdavi <mahdavi@psc.edu>
Pittsburgh Supercomputing Center Pittsburgh Supercomputing Center
4400 5th Avenue 4400 5th Avenue
Pittsburgh, PA 15213 Pittsburgh, PA 15213
USA USA
Vern Paxson <vern@ee.lbl.gov> Vern Paxson <vern@ee.lbl.gov>
MS 50B/2239 MS 50A-3111
Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory
University of California University of California
Berkeley, CA 94720 Berkeley, CA 94720
ID IPPM Metrics for Measuring Connectivity August 1998
USA USA
Phone: +1 510/486-7504 Phone: +1 510/486-7504
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